1. Introduction

Solving scientific problems requires data. It can be obtained by conducting experiments or sample surveys. The purpose of every sample survey is to obtain the information about populations by selecting the sample. Population is a group of units defined according to the objective of the survey. Here, the term ‘unit’ means the sampling unit which is the smallest element upon which the measurements are to be made for drawing the inferences. Examples of populations are all fields under a specified crop as in area, all agricultural holdings above specified size as in agricultural surveys, or the number of forest fringe villages in the country. The sample surveys are conducted by government and non-government organizations, researchers, sociologists, and business firms to get answers to certain specific questions which cannot be obtained directly through mathematical and statistical formulations. The sample surveys are conducted on demography (sex ratio), labor force (employment), health and living conditions, political opinion poll, marketing, etc. Surveys have thus grown into a universally accepted approach for information gathering. While conducting a sample survey, it should be conducted in such a way that inference related to the population should have a valid statistical background. A sampling method is a scientific and objective-oriented procedure of selecting units from the population. It provides a sample which may be truly representative of the population. Examples of samples are provided by a handful of grains taken from a sack, or a spoonful of rice taken from a pressure cooker.